[lttng-dev] [PATCH babeltrace] debug info: Call register_event_debug_infos for all events

[Jérémie Galarneau]

Merged as part of master and stable-1.4.

Thanks!
Jérémie

On Sun, Jun 19, 2016 at 11:14 AM, Simon Marchi <simon.marchi at polymtl.ca> wrote:
> The register_event_debug_infos function is responsible for setting the
> debug_info_src field of the struct definition_integer representing the
> "ip" context field.  This pointer is used later to print the
> source and binary location of the tracepoint.
>
> Currently, it's not called for the events that have a special meaning
> for the debug info analysis (statedump start, dlopen, bin_info, etc).
> This means that for these events, the debug_info_src pointer keeps the
> value of the previous event from that stream (since the ip field is in
> stream event context, there is one instance per stream), which leads to
> wrong information and/or crash.  A crash can happen when the debug info
> structures are cleared because a statedump start is encountered.
> debug_info_src becomes a stale pointer and babeltrace tries to print a
> string in free memory.
>
> The fix is to call register_event_debug_infos for all events, which will
> always set debug_info_src properly.  The events used to do the debug
> info analysis are still regular events and have their own location
> information.
>
> The trace in bug #1018 shows a crash caused by this issue.
>
> Here's an example of wrong info from the same trace:
>
> ... lttng_ust_statedump:bin_info: { cpu_id = 1 }, { vpid = 28991, ip = 0x7FD26665657D, debug_info = { bin = "libX11.so.6.3.0+0x213fa" } }, ...
> ... lttng_ust_statedump:build_id: { cpu_id = 1 }, { vpid = 28991, ip = 0x7FD266656656, debug_info = { bin = "libX11.so.6.3.0+0x213fa" } }, ...
>
> We can see that the ip values are different, but the debug info refers
> to the same location, which is impossible.  Here's the result with this
> patch applied.
>
> ... lttng_ust_statedump:bin_info: { cpu_id = 1 }, { vpid = 28991, ip = 0x7FD26665657D, debug_info = { bin = "liblttng-ust.so.0.0.0+0x3557d", func = "trace_bin_info_cb+0xfa" } }, ...
> ... lttng_ust_statedump:build_id: { cpu_id = 1 }, { vpid = 28991, ip = 0x7FD266656656, debug_info = { bin = "liblttng-ust.so.0.0.0+0x35656", func = "trace_build_id_cb+0xbc" } }, ...
>
> which seems more reasonnable.
>
> Signed-off-by: Simon Marchi <simon.marchi at polymtl.ca>
> ---
>  lib/debug-info.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/lib/debug-info.c b/lib/debug-info.c
> index aa19ce4..02ae582 100644
> --- a/lib/debug-info.c
> +++ b/lib/debug-info.c
> @@ -795,11 +795,11 @@ void debug_info_handle_event(struct debug_info *debug_info,
>         } else if (event_class->name == debug_info->q_statedump_build_id) {
>                 /* Build ID info */
>                 handle_statedump_build_id_event(debug_info, event);
> -       } else {
> -               /* Other events: register debug infos */
> -               register_event_debug_infos(debug_info, event);
>         }
>
> +       /* All events: register debug infos */
> +       register_event_debug_infos(debug_info, event);
> +
>  end:
>         return;
>  }
> --
> 2.8.3
>
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-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com